The biosynthesis, interconversion and regulatory functions of purine 5'-monophosphates will be studied. The enzyme adenylosuccinate synthetase exists as different isozymes; each with specific functions and regulation in various tissues. Chemical, physical and regulatory investigations will be conducted with the different isozymes. Localization aed regulation of the purine biosynthetic pathway will be evaluated. Other enzymes including pyruvate carboxylase, aspartase and 3-phosphoglycerate kinase will be studied. Alteration of nucleotide metabolism has adverse affects in both lymphoid and neoplastic cell proliferation and function. Previous studies in these laboratories have demonstrated that elimination of nucleotides from the diet alters purine metabolism. Preliminary experiments suggest that this dietary restriction influences the immune response as manifested by evaluation of the response of transplantable tumors and fetal heart allografts in animal models. The proposed studies will assess the effect of dietary nucleotides with and without added immunosuppressants on the immune response in mice fed various diets. Nucleotide depletion of tumor cells may alter their rate of growth and susceptibility to chemotherapy. The effect of dietary nucleotides with or without 6-mercaptopurine or other anti-tumor drugs on the growth of transplantable tumors in mice and rats will be studied. Dietary effects will be correlated with alterations in purine and pyrimidine metabolism in ascites tumor cells. Finally, the mechanism of the enhanced effect of purine or pyrimidine antimetabolites by diet will be studied in an ascites tumor using high pressure liquid chromatography to determine metabolite levels. A nucleotide free diet, based on our preliminary results, may enhance the effects of chemotherapeutic agents in autoimmune, neoplastic and viral disease states and have a positive influence on organ transplants.